That way you add "alien" methods to your data structures, which are the wrappers I wrote about.

The problem with wrappers is that they aren't very re-usable. In the example above you assumed that the sub what_does_it_return is in your own code base, or easily overridable. That's not necessarily the case. So you have to hope that whoever wrote the module you're using has built proper, reusable and maintainable wrappers.

In contrast when you have introspection built into your language's OO model, you can just use that, and it will work fine.

Another problem with overloading is that it doesn't scale very well. If you have a million data objects, why should you overload them all if you just want to call a method on one of them?

Both of my points have in common that you need to plan in advance. You need to know or guess how the result objects of, for example, a de-serializer will be used. But you can't, because in the general case the one who uses your module is cleverer that you and, and more creative, and most of all he's crazier. He'll get some weird ideas of what to do, and there won't be wrappers in place, so he'll have to resort to something different.

So runtime introspection is at once lazy and humble - lazy because you don't try to guess in advance all use cases, and humble because you don't think you can guess them all.

That's the reason why Perl 6 has a pluggable object model that allows introspection - if something is missing or gone wrong, it's relatively easy to add, fix or replace afterwards.

In reply to Re^3: Runtime introspection: What good is it? by moritz
in thread Runtime introspection: What good is it? by BrowserUk

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